Flaps behavior

[Puma257]

First post so hello to all and to the developers THX for nice aircraft

Now the question.

I notice when using flaps to my very amazement lift decreases and speed increases.
How is that possible?? I'm not going to dispute the flight dynamics - they gotta be right - I'm just curious what kind of flight dynamics are behind this.

Regards,

Puma

[maherd]

Hi Puma, good question
I suspect what you’re actually seeing is the effect of flap's on your pitching moment.
As you’d expect on a low wing aircraft adding flaps causes the nose to pitch down.
(generally high-wing aircraft want to pitch up with flaps)
So you’ll need to account for that as you flight test.
The flaps initially increase lift, drag, and down moment; and at 100% the effect is dominated by drag and moment.
One simple way to isolate flap effects is to use the autopilot to maintain your altitude.
Allow for enough time after reconfiguring to let the forces stabilize.
It’s tricky to get a power setting low enough to extend flaps clean, yet high enough to hold an alt with flaps…because the aircraft will transition into slow flight. It’ll want more power.
But to observe the flap effects in isolation both power and alt must remain constant.
Another way to watch the flap effects empirically is to use a tool like AFSD.
Danny

[Puma257]

Hi Maherd,

So these RV7 flaps have some kind of "opposite" effect... Most peculiar!
This begs the very next question:

I did some CG calculations with me as the only passenger weighing 178LBS, full tanks, A category, and as was the case I found out I was rather nose heavy; but within CG range.
May I conclude, for this situation, that using flaps can get me out of healthy CG range?
(I could not provoke such condition sofar.)

regards,

Puma

[maherd]

So these RV7 flaps have some kind of "opposite" effect... Most peculiar!

I suppose you could say...although it's not quite how I'd put it In either a high-wing or low-wing a pilot trims for flaps...and actively manages pitch (as they're reconfiguring). So set flaps and re-trim for speed. Generally...high-wing aircraft will want to deviate pitch up; and low-wing aircraft will want to deviate pitch down.

You’re other comment is a bit of a brain teaser. Offhand I’d imagine the effect isn’t so significant to be a real concern…and certainly accounted for in the design and CG envelope. But as an idea, I think the effect would aggravate a nose-heavy aircraft as you suggested. Also, a rear CG is more critical and in that case a high-wing-flap would aggravate a rear CG…maybe even bring on a stall. The low wing simply drops the nose and builds more speed.